The present invention is directed to liquid developer compositions suitable for the development of electrostatic latent images. More specifically, the present invention is directed to liquid developers having curable liquid vehicles. One embodiment of the present invention is directed to a liquid developer comprising a colorant and a substantial amount of a curable liquid vehicle having a viscosity of no more than about 500 centipoise and a resistivity of no less than about 10.sup.8 ohm-cm. In one specific embodiment, the invention comprises an electrophoretic liquid developer comprising a substantial amount of a curable liquid vehicle having a viscosity of no more than about 20 centipoise and a resistivity of no less than about 5.times.10.sup.9 ohm-cm, a charge control agent, and colored particles capable of becoming charged and migrating through the liquid vehicle to develop an electrostatic latent image. Another specific embodiment of the present invention is directed to a liquid developer suitable for polarizable liquid development comprising a colorant and a substantial amount of a curable liquid vehicle having a viscosity of from about 25 to about 500 centipoise and a resistivity of from about 10.sup.8 to about 10.sup.11 ohm-cm. Still another specific embodiment of the present invention is directed to a photoelectrophoretic liquid developer comprising a substantial amount of a curable liquid vehicle having a viscosity of no more than about 20 centipoise and a resistivity of no less than about 5.times.10.sup.9 ohm-cm, and photosensitive colored particles capable of becoming charged and migrating through the liquid vehicle upon exposure to radiation to form an image. Advantages of the present invention include the reduction or substantial elimination of solvent vapor emissions from copiers or printers employing these liquid developers, the reduction or substantial elimination of solvent vapor emissions from documents prepared by liquid development processes employing these liquid developers, and the reduction of solvent disposal from liquid development apparatuses.
Additional specific embodiments of the present invention are directed to liquid developers having curable liquid vehicles and heterogeneous polymerization initiators. One embodiment of the present invention is directed to a liquid developer comprising a colorant, a substantial amount of a curable liquid vehicle having a viscosity of no more than about 500 centipoise and a resistivity of no less than about 10.sup.8 ohm-cm, and solid particles containing an initiator substantially insoluble in the liquid vehicle and capable, upon activation, of initiating polymerization of the curable liquid vehicle. In one specific embodiment, the invention comprises an electrophoretic liquid developer comprising a substantial amount of a curable liquid vehicle having a viscosity of no more than about 20 centipoise and a resistivity of no less than about 5.times.10.sup.9 ohm-cm, a charge control agent, colored particles capable of becoming charged and migrating through the liquid vehicle to develop an electrostatic latent image, and solid particles containing an initiator substantially insoluble in the liquid vehicle and capable, upon activation, of initiating polymerization of the curable liquid vehicle. The solid particles may be the colored particles that become charged or may be particles of a material other than the colored particles that become charged. Another specific embodiment of the present invention is directed to a liquid developer suitable for polarizable liquid development comprising a colorant, a substantial amount of a curable liquid vehicle having a viscosity of from about 25 to about 500 centipoise and a resistivity of from about 10.sup.8 to about 10.sup.11 ohm-cm, and solid particles containing an initiator substantially insoluble in the liquid vehicle and capable, upon activation, of initiating polymerization of the curable liquid vehicle. Still another specific embodiment of the present invention is directed to a photoelectrophoretic liquid developer comprising a substantial amount of a curable liquid vehicle having a viscosity of no more than about 20 centipoise and a resistivity of no less than about 5.times.10.sup.9 ohm-cm, photosensitive colored particles capable of becoming charged and migrating through the liquid vehicle upon exposure to radiation to form an image, and solid particles containing an initiator substantially insoluble in the liquid vehicle and capable, upon activation, of initiating polymerization of the curable liquid vehicle.
Advantages of curable liquid developers include the reduction or substantial elimination of solvent vapor emissions from copiers or printers employing these liquid developers, the reduction or substantial elimination of solvent vapor emissions from documents prepared by liquid development processes employing these liquid developers, and the reduction of solvent disposal from liquid development apparatuses. The present invention, in which the liquid developers contain a heterogeneous polymerization initiator contained on or in solid particles in the developer, has the additional advantages of enabling polymerization of liquids with initiators not soluble in the liquid and elimination of the need for solubilizing solvents or derivatization of the initiator to render the initiator soluble in the liquid monomer. The use of a substantially insoluble initiator enables a wide range of choices of liquids and initiators. In addition, the use of a substantially insoluble initiator prevents adverse effects on the conductivity of the liquid vehicle as a result of the presence either of a soluble initiator or of an initially insoluble initiator and a solubilizing agent.
Curable inks are known in the printing industry. For example, U.S. Pat. No. 4,680,368 (Nakamoto et al.), the disclosure of which is totally incorporated herein by reference, discloses an ultraviolet curable ink composition comprising a polyurethane polymethacrylate obtained by reacting a polyisocyanate compound of the formula ##STR1## wherein R.sub.1 is a hydrogen atom or a methyl group, and n is an integer of from 1 to 20, with a hydroxyl group containing methacrylate and having in one molecule at least two methacryloyl groups and at least two urethane bonds, a radical polymerizable low molecular weight compound, and a photopolymerization initiator.
In addition, U.S. Pat. No. 4,443,495 (Morgan et al.), the disclosure of which is totally incorporated herein by reference, discloses a heat curable conductive ink which comprises ( 1) an ethylenically unsaturated member of the group consisting of (a) a liquid ethylenically unsaturated monomer, oligomer, or prepolymer of the formula ##STR2## wherein R is H or CH.sub.3, R.sub.1 is an organic moiety and n is at least 2, (b) a polythiol in combination with (a), a polythiol in combination with a liquid ethylenically unsaturated monomer, oligomer, or prepolymer of the formula ##STR3## wherein R.sub.2 is H or CH.sub.3, R.sub.3 is an organic moiety and n is at least 2, and (d) mixtures of (a), (b), and (c); (2) a thermal initiator; and (3) an electrically conductive material. Heating of the composition in a desired pattern on a substrate results in a printed electric circuit.
Further, U.S. Pat. No. 4,751,102 (Adair et al.), the disclosure of which is totally incorporated herein by reference, discloses a radiation curable ink composition comprising pigment and a photohardenable composition, wherein the photohardenable composition comprises a free radical addition polymerizable or crosslinkable compound and an ionic dye reactive counter ion compound which is capable of absorbing actinic radiation and producing free radicals which initiate free radical polymerization or crosslinking of the polymerizable or crosslinkable compound.
Additionally, U.S. Pat. No. 4,334,970 (Lombardi et al.), the disclosure of which is totally incorporated herein by reference, discloses a photosensitive resin system that is essentially solvent free and contains an ester produced from an unsaturated organic acid and a polyhydroxyl containing material, a photoinitiator, a carbonyl initiator, a monomer capable of reacting with an acrylic monomer, and an unsaturated hydroxyl containing polymer hydrocarbon.
Further, "Photochemical Aspects of UV Curing," Y.C. Chang, Photographic Science and Engineering, Vol. 21, No. 6 (1977) discloses the electro-optical properties of UV-curing materials, the effect of pigment dispersion on the curing rate of inks containing pigments, and the spectroscopic calibration of the degree of UV cure.
U.S. Pat. Nos. 3,661,614, 4,003,868, and 4,215,167, the disclosures of which are totally incorporated herein by reference, also disclose ultraviolet curable printing inks.
U.S. Pat. No. 4,399,209 (Sanders et al.), the disclosure of which is totally incorporated herein by reference, discloses a transfer imaging system wherein images are formed by imagewise exposing a layer comprising a chromogenic material and pressure rupturable capsules containing, as an internal phase, a photosensitive composition. When a coated composition containing the chromogenic material and the encapsulated photosensitive composition is exposed to actinic radiation and the capsules are subsequently ruptured in the presence of a developer, the image-forming reaction between the chromogenic material and the developer discriminately occurs in the exposed or unexposed areas and produces a detectable image. This result is accomplished by controlling whether the chromogenic material can transfer from the imaging sheet to the developer sheet. Generally, the photosensitive composition has a viscosity that changes upon exposure to actinic radiation such that upon exposure there is a change in the viscosity of the internal phase in the exposed areas which imagewise determines whether the chromogenic material is accessible to the developer. The photosensitive composition may be a radiation curable composition which, upon exposure to light, increases in viscosity and immobilizes the chromogenic material, thereby preventing it from transferring to the developer sheet and reacting with the developer material. Alternatively, the chromogenic material can be encapsulated with a substance which is depolymerized or otherwise decreased in molecular weight upon exposure, resulting in a decrease in viscosity which renders the chromogenic material accessible or transferrable to the developer in the exposed areas.
Liquid developers and liquid development processes for the development of electrostatic latent images are also known. In electrophoretic developers and processes, the liquid developers generally comprise a liquid vehicle and colored toner particles, and frequently also contain a charge control agent. The colored toner particles become charged, and upon contacting the electrostatic latent image with the liquid developer, the particles migrate through the liquid vehicle toward the charged image, thereby effecting development. Any residual liquid vehicle remaining on the image subsequent to development is evaporated or absorbed into the receiving sheet. Typically, liquid developers employ hydrocarbon liquid vehicles, most commonly high boiling aliphatic hydrocarbons that are relatively high in resistivity and nontoxic. Developers and processes of this type are disclosed in, for example, U.S. Pat. Nos. 4,476,210, 2,877,133, 2,890,174, 2,899,335, 2,892,709, 2,913,353, 3,729,419, 3,841,893, 3,968,044, 4,794,651, 4,762,764, 4,830,945, 4,686,936, 4,766,049, 4,707,429, 4,780,388, 3,976,808, 4,877,698, 4,880,720, 4,880,432, and copending application U.S. Ser. No. 07/300,395, the disclosures of each of which are totally incorporated herein by reference.
In polarizable liquid development processes, as disclosed in U.S. Pat. No. 3,084,043 (Gundlach), the disclosure of which is totally incorporated herein by reference, liquid developers having relatively low viscosity and low volatility and relatively high electrical conductivity (relatively low volume resistivity) are deposited on a gravure roller to fill the depressions in the roller surface. Excess developer is removed from the lands between the depressions, and as a receiving surface charged in image configuration passes near the gravure roller, liquid developer is attracted from the depressions onto the receiving surface in image configuration by the charged image. Developers and processes of this type are disclosed in, for example, U.S. Pat. Nos. 4,047,943, 4,059,444, 4,822,710, 4,804,601, 4,766,049, Canadian Patent 37,823, Canadian Patent 926,182, Canadian Patent 942,554, British Patent 1,321,286, and British Patent 1,312,844, the disclosures of each of which are totally incorporated herein by reference.
In photoelectrophoretic liquid development processes, as disclosed in, for example, U.S. Pat. Nos. 4,135,925, 3,383,993, 3,384,488, 3,384,565, 3,384,566, 4,043,655, and 4,023,968, the disclosures of each of which are totally incorporated herein by reference, colored photosensitive toner particles are suspended in an insulating carrier liquid. The suspension is placed between at least two electrodes subjected to a potential difference and exposed to a light image. Typically, the imaging suspension is placed on a transparent electrically conductive support in the form of a thin film and exposure is made through the transparent support while a second biased electrode is rolled across the suspension. It is believed that the particles bear an initial charge once suspended in the liquid carrier which causes them to be attracted to the transparent base electrode upon application of the potential difference. Upon exposure, the particles change polarity by exchanging charge with the base electrode so that the exposed particles migrate to the second or roller electrode, thereby forming images on each of the electrodes by particle subtraction, each image being complementary one to the other. Both polychromatic and monochromatic images can be formed by the process; when polychromatic images are prepared, the liquid developer can contain toner particles of more than one color.
The following publication has been discovered and is believed to be of background interest with respect to the present application. C.C. Chow, "Ultra-Violet Curable Liquid Immersion Development Toner," Xerox Disclosure Journal, Volume 1, Number 5, page 49 (1976) discloses a liquid immersion development process using a toner consisting of a viscous ultraviolet curable liquid polymer, said toner being dispersed in a carrier fluid and used in the conventional way. The print is exposed to ultraviolet light to convert the liquid toner into a non-tacky solid. The carrier fluid is then evaporated from the imaging member surface by warm air and condensed within the copying machine. The ultraviolet curable polymer is then transferred to paper and fixed by exposure to ultraviolet radiation. The process is such that solvent recovery is necessary only inside the machine and solvent does not become absorbed into the paper.
Additional liquid developers containing curable resins in a liquid vehicle, such as an aliphatic hydrocarbon, are as disclosed in Japanese Patent 62-115 171, Japanese Patent 62-018 575, Japanese Patent 62-018 574, Japanese Patent 61-156 264, Japanese Patent 61 - 156 263, Japanese Patent 61-156 262, Japanese Patent 61-156 261, Japanese Patent 61-060 714, Japanese Patent 63-155 055, and Japanese Patent 62-098 364. In addition, U.S. Pat. No. 4,764,447, Japanese Patent 62-007 718, Japanese Patent 62-007 717, Japanese Patent 62-007 716, Japanese Patent 62-004 714, Japanese Patent 61-020 056, and Japanese Patent 60-249 156 disclose processes for polymerizing monomers in a hydrocarbon liquid vehicle to form dispersions of polymer particles suitable for use as liquid developers. Further, Japanese Patent 62-014168 discloses an encapsulated toner contained in a liquid vehicle. The capsule core can be cured by heat, and the monomers or oligomers become fixed to paper when images developed with the developer are cured.
Further, heterogeneous catalyst systems are known. For example, U.S. Pat. No. 4,677,137 (Bany et al.), the disclosure of which is totally incorporated herein by reference, discloses supported initiators for the radiation activated polymerization of cationically polymerizable compounds, particularly epoxide group containing compounds. The supported initiators comprise a particulate carrier and a photocatalytic ionic salt. The supported initiators are particularly useful for the polymerization of cationically polymerizable compounds in which the ionic salt alone is not soluble; the initiator is supported on dispersible carrier material, which overcomes the problem of insolubility in epoxypolysiloxane.
In addition, U.S. Pat. No. 3,513,109 (Stiles), the disclosure of which is totally incorporated herein by reference, discloses a method of applying catalytic materials to a support, particularly supports having smooth surfaces of low surface area, by slurrying a finely divided form of the catalytic material in a solution of a metal ammine, applying the slurry to the support, drying, and calcining. In a preferred aspect, the catalytic material applied contains interspersants to stabilize the catalyst from crystal growth at high temperatures.
One difficulty frequently encountered with the use of liquid electrophoretic developers is an objectionable odor that typically accompanies liquid development processes. The sources of this odor are solvent vapors emitted from the copier or printer and the slow release of vapor from residual liquid vehicle remaining on the receiver sheet. A file drawer containing several documents prepared by liquid development processes can accumulate vapor to an unacceptable level. Accordingly, the reduction of solvent vapor emissions from liquid developing machines and from prints prepared with liquid developers is highly desirable for environmental and aesthetic purposes. These difficulties can be overcome with liquid developers having curable liquid vehicles. Curable liquid developers and development processes employing curable liquid developers can produce prints with little or substantially no odor, reduce or substantially eliminate the emission or carryout of solvent vapors from copiers and printers employing liquid development processes, reduce or eliminate the need to dispose of solvents from a copier or printer employing liquid development, enable formation of images with excellent fix to a substrate, and enable simplified containment and capture procedures for reducing or eliminating solvent emissions for copiers or printers employing liquid development.
A difficulty remains, however, with respect to curable liquid developers in that curable liquids suitable for use as the vehicle in a liquid developer are limited since the curable liquid must meet stringent viscosity and conductivity requirements. When the liquid is cured by polymerization via a homogeneous initiator, the choice of liquid vehicle is further restricted to liquids in which a suitable polymerization initiator is soluble, or restricted to those soluble initiators that do not force the conductivity value of the liquid vehicle outside of the desired range, or for which suitable solubilizing solvents or derivitazation of the initiator can render a suitable initiator soluble in the liquid.
Although known materials are suitable for their intended purposes, a need continues to exist for liquid developer compositions that produce prints with little or substantially no odor. A need also remains for liquid developer compositions that reduce or substantially eliminate the emission or carryout of solvent vapors from copiers and printers employing liquid development processes. Further, there is a need for liquid developer compositions that have curable liquid vehicles and that enable generation of high quality images. Additionally, a need exists for liquid developers and liquid development techniques that reduce or eliminate the need to dispose of solvents from a copier or printer employing liquid development. Further, there is a need for liquid developers and liquid development processes that enable formation of images with excellent fix to a substrate. In addition, a need remains for liquid developers and liquid development processes that enable simplified containment and capture procedures for reducing or eliminating solvent emissions for copiers or printers employing liquid development. Additionally, a need remains for curable liquid developers containing an initiator in substantially insoluble form. In addition, a need remains for curable liquid developers for which the choice of suitable vehicles is expanded. Further, there is a need for curable liquid developers for which no solubilizing solvent is required to solubilize the polymerization initiator in the monomer. A need also remains for curable liquid developers for which there is no need to prepare a derivative of a suitable initiator for the purpose of rendering the initiator soluble in the monomer. Additionally, a need exists for curable liquid developers containing heterogeneous initiators for which the desired developer color, hue, and tint remain unimpaired.